1. Field of the Invention
The present invention relates to a position detecting device and a position detecting method for detecting a position indicated by a position indicator, such as a stylus pen.
2. Description of the Related Art
Examples of known position detecting devices are disclosed in Japanese Unexamined Patent Publication No. S63-70326 and Japanese Unexamined Patent Publication No. H07-175572 (corresponding to U.S. Pat. No. 5,679,930, incorporated by reference herein), which have already been put into practical use. With such devices, a position indicated by a position indicator is detected by providing a resonant circuit in the position indicator to transmit/receive electromagnetic waves between the position indicator and a tablet, over which a user moves the position indicator. With some position detecting devices, extremely good operability is achieved by making the position indicator cordless and battery-free.
In some cases, it is desirable to incorporate position detecting technology into a device having a liquid crystal display. By incorporating a position indicator into a handheld stylus pen, a user is able to perform input operations by directly writing with the stylus pen at a desired drawing place on the liquid crystal display screen. The position detecting devices generally include a sensor having a number of coils that transmit and receive signals from the position indicator. In the past, it has not been practical to put the sensor coils (also referred to as a sensor pattern) on a front surface of the liquid crystal display, because the sensor coils are not very transparent.
For this reason, in related apparatuses in which a liquid crystal display device and a position detecting device are integrated, the aforesaid sensor coils are arranged in the rear of the liquid crystal panel. Due to such an arrangement, the once-assembled liquid crystal panel needs to be disassembled for assembling the sensor coils, thereby increasing cost and manufacturing complexity. Furthermore, the liquid crystal panel can not be easily replaced.
Thus, there is an increasingly strong demand for making the sensor coils of the position detecting device transparent so that the coils can be disposed on the front surface of the liquid crystal panel. An ITO film (Indium Tin Oxide film) is widely known as a transparent conductive material for forming the sensor coils. However, since the ITO film has high resistance, if the sensor coils are formed by the ITO film, it will be difficult to transmit sufficient power to the position indicator by using such sensor coils.
To solve such a problem, there is a proposal to provide a transmittance coil for transmitting a drive signal to the position indicator in the periphery of the position detecting area of the position detecting device. For example, it is disclosed in Japanese Unexamined Patent Publication No. H05-88811 (incorporated by reference herein) that a transmittance coil is provided to surround the periphery of the position detecting area of a tablet-like position detecting device.